Index / Aggregate formula with Search - excel

Question

I have a sample data (1,2,3,4) on A2:D2 columns and on F1, I have (1,3), and on G1 (2,3,4).
I was suggested to use this formula
=INDEX($A2:$D2,AGGREGATE(15,6,ROW($A2:$D2)/ISNUMBER(SEARCH(TEXT($A2:$D2,"000,"),F$1&",")),1))
on F2, and G2 which is supposed to give the matching values on F2 and G2 respectively. Since both values (1,3) match, the result should be (1,3) on F2, and (2,3,4) on G2.
So basically this formula is supposed to work like index/match formula but instead of single values, it works on comma separated 2 or 3 values.
When I try to use the formula I keep getting #NUM! error. Can I get a little help to make this formula work, please?
Thanks.
Note: I am open to alternative solutions, but if it requires VBA, it has to be with a user defined formula. Without UDF, it is not useful for me.

Answer 1

A UDF should look like this
Option Explicit
Function MultFind(r As Range, s As String) As String
Dim c As Range
Dim result As String
For Each c In r
If InStr("," & s & ",", "," & c & ",") <> 0 Then result = result & c & ","
Next c
If Len(result) > 0 Then result = Left(result, Len(result) - 1)
MultFind = result
End Function
Called as
=MultFind($A2:$D2,F1)
Edit
Here it is with optional parameter for delimiter:
Option Explicit
Function MultFind(r As Range, s As String, Optional delimiter As String = ",") As String
Dim c As Range
Dim result As String
' Check each cell in range against search string
For Each c In r
If InStr(delimiter & s & delimiter, delimiter & c & delimiter) <> 0 Then result = result & c & delimiter
Next c
' Delimiter may be more than one character
If Len(result) > 0 Then result = Left(result, Len(result) - Len(delimiter))
MultFind = result
End Function